Measuring and wirelessly transmitting temperature, air/environmental humidity, soil moisture or pressure with ultra-low monetary cost (in dollars), as well as ultra-low power cost (in microWatts) is typically required in a variety of emerging applications. For example, batteryless soil moisture and/or air humidity sensing or plant electric potential with a large number of wireless devices is required in agriculture and environmental sensing; wireless and low-cost measurement of tire pressure in automobiles, including cars and bicycles, is another application domain. Large numbers of such wireless sensors require an extensive amount of money to acquire, install, operate and maintain. Moreover, their power consumption in continuous operation may not allow for batteryless operation or may require battery replacements periodically, or may increase cost for energy storage devices, such as supercapacitors.
Conventional wireless sensing devices require interfacing a sensing circuit to an analog-to-digital converter (ADC), followed by a digital communication Marconi radio; the latter is typically controlled by a digital logic chip (DLC) or an embedded microcontroller unit (MCU). Such designs increase monetary (in Euros) and power cost (in Watt) per wireless sensor, while they require a dedicated wireless receiver of the sensed and wirelessly-transmitted information. In the prior art [Bletsas et al 08] scatter radio is disclosed, i.e., communication by means of reflection, for each sensor, equipped with ADC and DLC or MCU, decreasing the overall monetary and energy cost. In [Bletsas et al 12], [Bletsas et al 12b], [Bletsas et al 14] illuminator of sensor and receiver of the scattered (from the sensor) information are distinct units; alternatively, the illuminator can be a broadcasting TV [Smith et al 13] or FM [Smith et al 17] station, with sensor modulating bits with appropriate DLC and scatter radio; in [Bletsas et al 13], [Bletsas et al 13b], [Bletsas et al 14b] analog signals are modulated with scatter radio, where a dedicated continuous wave (CW) carrier device is utilized as the illuminating source and sensed information is received, processed and extracted from a dedicated software-defined radio (SDR) receiver. Thus, prior art has either used analog scatter radio with dedicated illuminators and receivers or digital scatter radio, with sensors equipped with DLC or MCU, requiring also an ADC to interface specific sensors.
Dedicated emitters or receivers for scatter radio increase the overall monetary cost to assembly, operate and maintain scatter radio infrastructure. Scatter radio-based sensors may also suffer from limited communications range. Furthermore, MCU and/or DLC and/or ADC increase complexity and thus, monetary and power cost per wireless sensor.
Therefore, a need exists to improve the design of sensing devices and receivers of sensor signals in order to jointly reduce wireless sensor power consumption and monetary cost, while being able to receive the information several meters away.
The inventors have devised a backscatter sensor device and a receiver device method of sensor signals that improve over the prior art. More specifically, this invention offers a complete, ultra-low power and ultra-low cost analog system, able to measure a physical quantity via a capacitive or resistive sensing element; the invented sensor exploits either dedicated or ambient illuminating sources (FM broadcasting stations) in order to scatter the measured value to a conventional FM radio receiver, including FM radio equipped smartphones. The wireless sensor presented consumes below 24 μW at continuous operation and is build using very low cost, off-the-shelf components. Additionally, a device method in conjunction with commodity electronics FM receiver offers communication ranges in the order of 26 meters outdoor.